The present invention relates to a circuit arrangement for establishing and terminating a connection with the aid of a data transmission device.
Such arrangements have become known, for example, as video text modems, in the development and planning of a new service, in Great Britain called viewdata such as disclosed, for example, in Federal Republic of Germany patent application Nos. P 28 23 283, 28 40 845 and 29 42 441 and in an article entitled "Funktion der Teilnehmereinrichtungen f/u/ r Bildschirmtext" [Operation of Subscriber Devices for Video Text] by Bambach, Koeck, Sch/u/ ssler, in Fernmeldepraxis [Telecommunications Practice], Volume 56/1979, No. 24.
Such video text modems, which are equipped with automatic selection, or dialing, devices, together with a television receiver equipped for video text reception, allow the owner or user of a telephone terminal to be provided with the new viewdata service over his telephone line. However, telephone conversations and video text reception are possible only alternatively.
In view of a requirement by the Federal Postal Service of the Federal Republic of Germany, video text modems must be equipped with a current supply which is independent of the electric power utility service; they are therefore fed through the subscriber's telephone connection line itself.
When establishing a video text connection it is possible that temporary supply current interruptions or reductions occur which may have the result that the establishment of the connection is interfered with and the subscriber may have to restart the procedure. Depending on the time spent by the individual subscriber in such a case, this may occupy important parts of the exchange equipment for unnecessarily long periods of time. This aspect is of particular importance when video text modems are used in automatic branch exchanges.